The present invention relates to hydraulic valves.
The invention concerns a hydraulic valve arrangement with a control valve, which, in a first operating position, connects a motor connection with a pump connection, in a second operating position, connects a motor connection with a tank connection, and, in a locking position, disconnects the motor connection from the pump and tank connection, and with a locking valve coupled between the control valve and the motor connection, dividing the motor line into a first section allocated to the control valve and a second section allocated to the motor connection, a pressure release valve made as a seated valve being provided for the locking valve, the operating element of said pressure release valve being loaded in the closing direction by the pressure in the first section and a spring and in the opening direction by a constant control pressure acting in dependence of the position of the control valve and, when operated, releasing the pressure in a spring chamber acting in the closing direction of the locking valve to the first section.
A valve arrangement of this kind, produced by the company Bosch, has been marketed by the company Deutz Fahr. It serves the purpose of displacing a motor in the lifting direction by means of oil pressure and in the opposite direction by means of the load. In this connection, the locking valve is controlled in such a way that a constant lowering speed occurs. The pressure release valve is integrated in the locking valve, the seat of the pressure release valve being arranged in the front wall of the locking valve piston. To ensure generation of the constant control pressure, a branching of a channel leading to the tank is provided immediately next to the operating member of the pressure release valve, said channel having a spring loaded locking valve.
The invention is based on the task of providing a hydraulic valve arrangement as described in the introduction, which has an improved control behaviour.
According to the invention, this task is solved in that the seat of the pressure release valve is fixed to the housing.
With this design, a more stable control is ensured. Firstly, the pressure areas of the pressure release valve and the locking valve are completely independent of each other. Secondly, the operating member of the pressure release valve does not have to follow the load-dependent movement of the locking valve piston, so that the changes of the spring force of the spring belonging to the operating member of the pressure release valve are smaller.
It is advantageous that the pressure release valves are lifting valves with piston-shaped operating elements, arranged in housing bores of a module containing the locking valves. This gives a simple design.
It is also advantageous that the constant control pressure is a continuously generated system pressure, which is supplied in dependence of the position of the control valve. Such a system pressure, which is often already available for other reasons, does not have to build up first, but is practically immediately available. Further, this simplifies the design, as it is not required for each valve module to comprise a constant pressure source.
In a preferred embodiment it is ensured that a system pressure source is formed by the outlet of a pressure valve supplied by the pump pressure, said pressure valve being loaded in the closing direction by the outlet pressure and in the opening direction by the tank pressure and a spring. Such a system pressure source supplies a system pressure of a high constancy.
Such a system pressure source can also be used in connection with a load pressure controlled pump.
A further development of the invention ensures that a second motor connection, a second locking valve and a second pressure release valve are provided for the operation of a motor in both directions.